SA election: Opposition leader casts early vote

South Australian Opposition Leader Steven Marshall has cast his vote more than a week out from the state election.

The member for Dunstan said he was entitled to vote early because he will be busy campaigning on polling day.

Liberal leader Steven Marshall has cast an early vote in the South Australia election. (AAP) ()Mr Marshall said he would be busy campaigning on polling day next Saturday. (AAP) ()

"There have been changes to the laws to allow us to be on booths handing out how-to-vote cards - that's what I'm going to be doing the entire way through March 17," he told reporters on Tuesday.

Despite pre-polling opening on Monday, campaign costing documents are not scheduled to be released until next week.

Costing documents have still not been released. (AAP) ()

Mr Marshall shut down the suggestion the release be brought forward so that pre-poll voters are fully informed.

"It's difficult to put the campaign costing document out early because we still do have campaign commitments and policies that we will announce that we don't want to foreshadow in the campaign costing document," he said.